1. Field of the Invention
The present invention relates to vertical alignment liquid crystal displays (LCDs), and more particularly to a continuous domain vertical alignment type of liquid crystal display.
2. Description of Prior Art
A liquid crystal display utilizes the optical and electrical anisotropy of liquid crystal molecules to produce an image. The liquid crystal molecules have a particular passive orientation when no voltage is applied thereto. However, in a driven state, the liquid crystal molecules change their orientation according to the strength and direction of the driving electric field. A polarization state of incident light changes when the light transmits through the liquid crystal molecules, due to the optical anisotropy of the liquid crystal molecules. The extent of the change depends on the orientation of the liquid crystal molecules. Thus, by properly controlling the driving electric field, an orientation of the liquid crystal molecules is changed and a desired image can be produced.
The first type of LCD developed was the TN (twisted nematic) mode LCD. Even though TN mode LCDs have been put into use in many applications, they have an inherent drawback that cannot be eliminated; namely, a very narrow viewing angle. By adding compensation films on TN mode LCDs, this problem can be ameliorated to some extent. However, the cost of the TN mode LCD is increased. Therefore, MVA (multi-domain vertical alignment) mode LCDs have recently been developed. In MVA mode liquid crystal displays, each pixel is divided into multiple domains. Liquid crystal molecules of a pixel are vertically aligned when no voltage is applied, and are inclined in different directions according to the domains when a voltage is applied. Thus MVA mode liquid crystal displays can provide wide viewing angles. Typical MVA mode liquid crystal displays have four domains in a pixel, and employ protrusions and/or slits at the pixels to achieve the desired effects.
Referring to FIGS. 6 and 7, Chinese Pat. Application No. 01,121,750, published on Jan. 23, 2002, discloses a four-domain MVA liquid crystal display. The MVA liquid crystal display 1 comprises a first substrate 11, a second substrate 12, a plurality of liquid crystal molecules 16 disposed between the first and second substrates 11, 12, and protrusions 111, 121 each having a triangular cross-section respectively disposed on the first and second substrates 11, 12. Components such as two polarizers having orthogonal polarization directions, pixel electrodes, common electrodes, thin film transistors and alignment films are also provided in the MVA liquid crystal display 1; however, these components are not shown in FIG. 6 or FIG. 7.
FIG. 6 shows the alignment directions of the liquid crystal molecules 16 when the MVA liquid crystal display 1 is in an off state; that is, when no voltage is applied. Most of the liquid crystal molecules 16 are vertically aligned perpendicular to the substrates 11, 12. Accordingly, light beams do not change their polarization states when passing through the liquid crystal molecules 16. The two polarizers are disposed on the substrates 11, 12 respectively. Because the polarization directions of the polarizers are orthogonal to each other, light beams transmitting from the first polarizer maintain their original polarization states and are absorbed by the second polarizer. In other words, the MVA liquid crystal display 1 is in a dark state when no voltage is applied.
FIG. 7 shows the orientation directions of the liquid crystal molecules 16 when the MVA liquid crystal display 1 is in an on state; that is, when a voltage is applied. An electric field perpendicular to the substrates 11, 12 is generated. Because the liquid crystal molecules 16 have negative dielectric anisotropy, they are oriented in directions perpendicular to the electric field. In addition, the protrusions 111, 121 affect the orientation of the liquid crystal molecules 16. For example, the liquid crystal molecules 16 at two opposite sides of the protrusion 111 are respectively oriented from top-right to bottom-left and from top-left to bottom-right. Therefore the light beams change their polarization states when passing through the liquid crystal molecules 16. Because the polarization directions of the polarizers are orthogonal to each other, the light beams with altered polarization states pass through the second polarizer. In other words, the MVA liquid crystal display 1 is in a white state when a voltage is applied.
FIG. 8 shows orientation directions of the liquid crystal molecules 16 in four domains A, B, C, D. The protrusions 111, 121 are arranged on the substrates 11, 12 along generally V-shaped paths. Liquid crystal molecules 16 at two opposite sides of the upper portions (as viewed in FIG. 8) of the protrusions 111, 121 incline in C and D directions, while liquid crystal molecules 16 at two opposite sides of the lower portions (as viewed in FIG. 8) of the protrusions 111, 121 incline in A and B directions. The orientation directions of the liquid crystal molecules 16 in a same inter-protrusion region are consistent. The orientation direction of the liquid crystal molecules 16 in each same inter-protrusion region is orthogonal to the orientation directions of the liquid crystal molecules 16 in all of the other inter-protrusion regions. Therefore, each pixel attains a visual effect that is an overall result of four domains. This gives the MVA liquid crystal display 1 a more even display performance at various different viewing angles.
However, the four-domain configuration can only compensate visual performance in four directions. The overall viewing angle characteristics of the MVA liquid crystal display 1 are still inherently limited, and the MVA liquid crystal display 1 cannot satisfactorily present a uniform display at all viewing angles.
It is desired to provide a vertical alignment mode liquid crystal display which overcomes the above-described problems.